In the heavy industry, large and heavy products can be difficult to handle manually. Thus, a hoist connecting to a clamping device can be used to lift and move heavy objects. An object can be clamped to a clamping device that is coupled to a hoist. The hoist can lift the object to a certain height, and then transfer to a proper location.
The clamping devices can utilize a mechanism that converts the weight of the object into a clamping force, thus the holding force on the object exerted by the clamping devices can be proportional to the weight of the object. A loading and unloading device, such as a crane or a hoist, can be coupled to the clamping device for lifting and transferring the objects.
A prior art clamping device can include a gripping device normally fabricated from structural steel components, that are designed to securely hold and lift construction materials though a scissor movement. The gripping device can use freely rotating pin connections to create a scissor configuration with two scissor arms. A first end of the scissor arms is configured to rotate towards each other in reaction to the opposite second end of the scissor arms being lifted vertically. The first end of the scissor arms rotate inwards and generate a compression force clamping on the object to be lifted. Essentially, the weight of the object is used to generate this clamping action.
Disadvantages of the gripper devices can include large sizes due to the long arms. For example, if the friction coefficient between the holding pads and the object is about 0.2, then a five times the weight of the object is needed to hold the object. In other words, the ratio of the upper arms and the lower arms is also about five to obtain the holding force. Other disadvantages can include multiple moving parts, such as the two arms forming the scissor action, together with operation complexity, especially during the time of loading and loading.